1. Field of the Invention
The present invention relates to a focus position adjustment method and system thereof, and more particularly to a focus position adjustment method and system thereof for an optical storage device.
2. Description of the Prior Art
A conventional optical disc drive apparatus comprises an optical pickup head for generating a laser beam to converge to an optical disc and receiving a laser beam reflected from the optical disc. The optical disc drive apparatus performs focus servo and tracking servo in order to accurately read or write data on the optical disc. The focus servo refers to control the laser beam from the optical disc drive apparatus to the optical disc so that the laser beam can converge to a specific focus position. In the prior art, the focus servo is performed according to a focus error signal of a laser beam reflected from the optical disc. The focus error signal represents the shift from the focus position of the laser beam on the optical disc. When focus positions are different, different jitters are obtained. Generally, the smaller the jitter is, the more accurate focus position is obtained.
However, the focus servo of the prior art has many problems. First, in a conventional optical disc drive apparatus, the focus servo adjusts focus position by searching the maximum value of the reproduction signal or the minimum value of the jitter. However, both perform differently in different addresses or data areas so that errors usually occur. Besides, because the calculation process for the focus error signal, the jitter and the focus position is complicated, it is very time-consuming and energy-consuming to get the smallest jitter. Second, the focus servo control method of the prior art is used for single spiral land groove format (SS-L/GFMT) optical disc without distinguishing a land track and a groove track. Therefore, it is not able to provide accurate focus servo for the high-density optical disc. Third, in a conventional optical disc drive apparatus, it is not considered that the zero level of the focus error signal is not always the best focus position. Therefore, errors usually occur when reading data from the optical disc. About the problems of the prior art, please refer to U.S. Pat. No. 6,240,055, focus position adjustment device and optical disc drive apparatus.
The technology disclosed in U.S. Pat. No. 6,240,055 is used for solving the above problems. However, U.S. Pat. No. 6,240,055 still utilizes the smallest jitter to look for the best focus position; the process for the focus servo cannot be effectively speeded up.
Furthermore, the technology disclosed in U.S. Pat. No. 6,240,055 needs an error rate counter, an RF detector, and a complicated algorithm to calculate the best focus position. A lot of computing resource and time are needed. Moreover, if the optical disc is blank, there will be no reproduction signal for estimating the jitter. Therefore, the disclosed technology must record a test signal in a drive test area on the optical disc, then perform the above mentioned procedure.
The technology disclosed in U.S. Pat. No. 6,407,968, optical information recording/reproducing apparatus having focus error signal compensation, detects a variation value and compensates the focus error signal based on the variation value to obtain the optimal focus position. The disclosed technology solves the time-consuming problem in conventional focus servo control.
Conventionally, when the optical disc drive apparatus reads an optical disc that is recorded with data, it goes through seeking track, tracking closed loop, and ON state of focus servo for reading each of the tracks on the optical disc.
The technology disclosed in U.S. Pat. No. 6,407,968 detects the variation value under the ON state of focus servo. The time for adjusting the focus position is increased. Besides, the variation value responses to a tracking error signal, and the tracking error signal and focus error signal are necessary for obtaining the variation value. Therefore, the technology disclosed in U.S. Pat. No. 6,407,968 is still time-consuming.
Therefore, the primary objective of the present invention is to provide a focus position adjustment method and system thereof to solve the problems in the prior art.